Sterically demanding bis(2‐silylindenyl)zirconium(IV) dichlorides as polymerisation catalyst precursors

Abstract

A set of different 1‐ and 2‐silyl‐substituted zirconocene dichloride/MAO catalyst systems was investigated with respect to their performance in ethene/1‐hexene copolymerisations. In‐depth studies of bis(2‐dimethylsilylindenyl) zirconium(IV) dichloride (1) revealed a multi‐site behaviour, illustrating sensitivity to the reaction temperature and the comonomer mole fraction. Surprisingly, an upper limit is observed for the latter, leading to complete catalyst inhibition. Analysis of the chain termination processes implies the possibility of a predominant, although in general less favourable, β‐hydride elimination route under certain polymerisation conditions.

On the Nonsingle-Site Character of Bis(2-Dimethylsilyl-indenyl)zirconium(IV) Dichloride/MAO and Bis(2-Trimethylsilyl-indenyl)zirconium(IV) Dichloride/MAO: Polymerization Characteristics and Mechanistic Implications

“…We did, however, find bimodal product distributions as the one depicted in Figure . Results on the presumably multimodal products of the series at 80 °C have been reported elsewhere 10b. Exhaustive Soxhlet extraction of the bimodal polymer sample, which was obtained at 30 °C and X H = 0.80 and presented in the aforementioned paper with the solvents diethyl ether, n -pentane, n -hexane, n -heptane, cyclohexane, and toluene afforded six fractions.…”

“…Because of the short lifetimes of the active sites, this claim remains difficult to verify, but a theoretical approach will be presented in the course of this contribution. Circumstantial evidence is given by the shape of the GPC elution curves, which reveal a temperature dependence (Figure ) 10b 2 GPC traces for 1b /MAO in ethene homopolymerizations at c( E ) = 0.14 mol/L at the temperatures 80, 60, 40, 30, 10 °C (from left to right). …”

“…Earlier and elsewhere, we have reported inter alia on the synthesis of bis(2-dimethylsilyl-indenyl)zirconium(IV) dichloride ( 1 ) and bis(2-trimethylsilyl-indenyl)zirconium(IV) dichloride ( 2 ) and preliminary polymerization studies. 10a,b Since then, we have been working further in this direction and wish to give a full account on the data obtained from ethene homopolymerization studies with 1 /MAO and 2 /MAO and ethene- co -1-hexene polymerization studies with 1 /MAO; conceptual quantum chemical considerations with regard to these systems shall also be mentioned.…”

“…Ethene- co -1-hexene Polymeriz ations. Earlier, we have reported trends in activity of different silyl-functionalized 1- and 2-substituted bis(indenyl)zirconocenes at a 1-hexene mole fraction of X H = 0.60 10b. The dependence of the polymer microstructure had been investigated, and we now wish to report on isothermal polymerization with a variation of the comonomer mole fraction in the feed.…”

“…Ethene Homopolymerizations. The effect of the silyl substituent on the polymerization activities has been investigated earlier and shall not be expanded further at this time 10a. For the homopolymerizations, we were interested in the catalyst's response to a change in temperature to investigate possible multisite behavior.…”